1. Field of the Invention
The present invention relates generally to positioning control systems and more particularly to a stepper actuator having a braking element configured to apply a braking force to mitigate unwanted rotation of the stepper actuator.
2. Description of the Prior Art
A positioning control system may be used in applications requiring accurate and precise regulation over the position of a given element. For instance, it may be desirable to have precise and accurate regulation over a control valve in a flow line carrying fluid at high pressure. Exemplary of such high pressure flow lines include the flow of gas or oil from a well, or the flow of high pressure steam to and from a turbine within a power plant. In an exemplary application, the control valve may be used to maintain the downstream pressure of the fluid in the flow line at safe and manageable levels.
Although precise regulation over a control valve in a high pressure fluid flow line may be desirable, it is often difficult to achieve. For instance, in certain applications, it is difficult to generate a sufficient amount of force to overcome the high pressure in the flow line to move the control valve at prescribed, accurate increments between its open and closed positions. In this regard, precise and accurate control over the fluid in the flow line may require small, incremental movements of the control valve, which is typically more difficult at high pressure.
To address this particular need, it is know in the prior art to employ the use of a hydraulic or pneumatic stepper actuator to achieve more precise and accurate positioning control over a fluid control valve. Known stepper actuators typically include a drive shaft which is adapted to be rotated in small increments. The rotation of the drive shaft corresponds to the incremental opening or closing of the control valve. In the prior art stepper actuators, the drive shaft is usually rotated by pneumatic or hydraulic actuation members. In certain prior art stepper actuators, the actuation members are mechanically connected to the drive shaft via a gear. The gear may be incrementally rotated by the actuation members through repeated engagement and disengagement of the actuation members to the gear, as needed to achieve incremental opening or closing of the fluid control valve. In this manner, the fluid control valve may be incrementally opened or closed to achieve desired flow parameters.
Once the fluid control valve is in the desired position, the actuation members of the prior art actuators are often disengaged from the gear. In this regard, one of the primary drawbacks of known stepper actuators is that upon such disengagement, forces are able to act on the drive shaft in a manner resulting in undesirable rotation thereof. As will be recognized, such rotation of the drive shaft, even in a small amount, may cause the fluid control valve to move from its desired position. For instance, vibration of the fluid control system may cause the drive shaft to rotate. As indicated above, such unwanted rotation of the drive shaft may compromise the precise control over the flow of fluid through the flow line.
Thus, there exists a need in the art for a stepper actuator having a braking mechanism configured to mitigate or prevent unwanted rotation of the stepper actuator, and in particular the drive shaft extending therethrough, upon the disengagement of the actuation members from the internal drive shaft rotational assembly (e.g., a gear) of the stepper actuator. The present invention addresses this particular need and others, as will be discussed in more detail below.